Trace, in the order I'm which they occur, the events that lead up to Macbeth's decision to murder Duncan.

The witches make a prophecy.  Macbeth receives the award of Thane of Cawdor.  Macbeth sends his wife a letter detailing what has happened thus far.  Duncan goes to Macbeth's castle.  Macbeth hesitates about killing Macbeth and Lady Macbeth talks him into her plan of murder.